Length compensating joints or telescoping joints are well known in the field of pipeline repair. Typically these apparatuses have been used onshore and offshore to allow for length adjustment when a section of pipeline is being replaced to minimize the amount of cutting and welding which is required. Particularly in offshore installations where access to the pipeline is difficult and costly, it is desirable that the length compensating joint be remotely operable with a reliable sealing means, preferably metal-to-metal. The present invention provides an improved seal structure which has these features.
The present invention is an improvement of the structure covered by the J. N. Troxell, Jr. U.S. Pat. No. 4,761,023. The Troxell telescoping joint discloses a metal-to-metal seal which can be energized or released by a pressure responsive means.
The W. M. Taylor et al. U.S. Pat. No. 4,720,124 discloses a telescoping joint with metal-to-metal sealing and locking surfaces disposed on the exterior and interior surfaces, respectively, of the inner and outer tubular members. Hydraulic pressure is used to disengage the sealing surfaces and provide relative movement between the inner and outer tubular members.
The T. R. Schmitz et al. U.S. Pat. No. 4,696,494 discloses an adjustable flowline joint which provides angular misalignment capability only and a hydraulically releasable locking means with metal-to-metal seals.
The J. E. Miller U.S. Pat. No. 4,436,325 discloses an adjustable locking coupling with metal-to-metal sealing and hydraulically actuated locking means. No provision is made for unlocking the coupling after installation.